An MBMS is a service that transmits multimedia contents packets acquired from a Contents Provider (CP) that is a data source or a multicast broadcast source server to multiple user terminals via a mobile communication network in broadcasting or multicasting scheme. In other words, the MBMS service refers to a service that transfers multimedia contents via the mobile communication network in a manner that external contents sources are linked with a Broadcast Multicast Service Center (BM-SC) that manages and controls the MBMS service and the BM-SC is linked with a Gateway General Packet Radio Service (GPRS) Support Node (GGSN) that operates as a gateway of packet data service in the mobile communication network.
This point-to-multipoint service simultaneously transfers MBMS contents from a CP/MB source server to a broadcast/multicast channel shared by multiple user terminals in a single broadcasting/multicasting transmission scheme, and thus can save the resources of the mobile communication network.
The MBMS service is provided by using mobile communication networks such as a Wideband Code Division Multiple Access (WCDMA) network, a Global System for Mobile communication (GSM) network, and so on.
FIG. 1 illustrates a system structure for offering an MBMS service based on the 3rd generation WCDMA network.
The MBMS service is offered depending on a location, which is called SA (Service Area). A service area to which the MBMS service is to be applied may have various sizes such as a cell area unit, one node B area unit, a Radio Network Controller (RNC) district area unit, a Serving GPRS Supporting Node (SGSN) area unit, a GGSN area unit, wherein different service areas may overlap with each other.
In a multimedia service, each of service areas SA1, SA2, and SA3 can offer a different MBMS service, and only user terminals or equipments (UEs) that have registered to receive the MBMS service while belonging to the corresponding service areas can receive the MBMS service.
In a broadcast service, however, all user terminals that belong to the corresponding service areas can receive the service. This is possible only when those user terminals that belong to the corresponding service areas designate channels for reception of such a broadcast service.
The 3rd generation wideband mobile communication network includes a Universal Mobile Telecommunications Network Terrible Radio Access Network (UTRAN) composed of a plurality of nodes B 101 for managing a plurality of user terminals and a plurality of RNCs for managing the plurality of nodes B 101, and a Core Network (CN) composed of a GGSN 104 connected to a plurality of SGSNs 103 providing a packet service.
A BM-SC 105, which is linked with the GGSN 104 of the mobile communication network, e.g., a WCDMA network, controls the MBMS to transmit contents to the plurality of user terminals singed in a multicast session that has registered the MBMS service through a distribution tree composed of link of the lower nodes of the GGSN 104 in a broadcasting or multicasting scheme.
A CP/MB source server 107 provides the broadcast multicast service contents of an internal contents provider and the broadcast multicast service contents of an external CP connected to the internet network depending on broadcast schedules by MBMS services.
The nodes B receive uplink signals transmitted form the plurality of user terminals in a physical layer level, and send downlink signals to the user terminals. That is, the nodes B transmit/receive signals to/from the user terminals, and serves as access points for connecting the user terminals to the UTRAN. The nodes B manages wireless resources of cell unit and communicate with the user terminals that exist within the corresponding cells over radio channels.
RNCs 102 are in charge of allocation and management of wireless resources for the plurality of nodes B, and serve as accession points for connecting the nodes B to the CN. Each of the RNCs 102 is connected to the SGSN 103 of the CN.
The SGSN 103 is connected to the GGSN 104 and manages the mobility of mobile terminals, and functions to selectively transmit data for MBMS related services to a specific RNC 102.
The GGSN 104 serves as a gateway for link with the internet or external packet network, and is connected to an external internet network via the following WCDMA system components and the BM-SC 105.
The BM-SC 105, which is a node that is in charge of MBMS service control, should be necessarily provided as one functional element of the WCDMA system for providing the MBMS service. The BM-SC 105, which serves as a subject of management and control for the MBMS service, offers the functions for preparation of services of MBMS user terminals and for delivery of service information. Further, the BM-SC 105 offers the functions of MBMS service subscriber and service information management, MBMS bearer service authentication in the mobile communication network, service start, and planning of MBMS information transmission and delivery thereof. An IP interface used when the GGSN 104 is connected to the external internet network is used for interface between the BM-SC 105 and the GGSN 104.
The BM-SC 105 functions as an access point to the CP/MB source server 106 to transfer the MBMS information and can serves as a contents provider itself.
The CP denotes a node including an application function of contents delivery and the MB is a node such as a storage which stores only contents or FTP server. The CP/MB source server can communicate in a node form over the public internet network.
If a user terminal registers a request for receipt of a desired MBMS service in the BM-SC 105, it receives the corresponding MBMS service contents from the BM-SC 105 at the start time of a specific MBMS service.
The BM-SC 105 transfers MBMS service contents from the CP/MB source server 106 to a plurality of user terminals in the corresponding service area SA1 through a common channel used in the service area via the mobile communication network by controlling the MBMS service. At this time, the BM-SC 105 transfers the corresponding contents to all the GGSNs 104 that support the user terminals that wish to receive the corresponding MBMS service.
FIG. 2 is a view for explaining a case of offering an MBMS service using several different mobile communication networks.
Specifically, FIG. 2 illustrates a situation where several mobile communication networks coexist in a certain area, wherein a service area of these mobile communication networks can overlap with each other. Each of the mobile communication networks may be a different network of a same or different wireless transmission scheme. These mobile communication networks include only GGSNs 201 to 204 that operate as a gateway for packet data service, wherein these GGSNs are linked with the BM-SC 105 for providing MBMS service. The BM-SC regards the mobile communication network as a transport network for transporting corresponding service contents that are not related to an area where a service is offered and a type of service to be offered, and therefore, is meant as a routing point where the GGSN represents the corresponding network exists at a lower stage on a multicast tree to which the service contents should be transported.
FIG. 3 is a functional block diagram of the BM-SC defined in the 3GPP standard.
In particular, FIG. 3 defines the functions to be performed in the BM-SC, wherein, in case of actually implementing the BM-SC, these functions can be mounted on physically different nodes. The BM-SC largely includes five functions as follows.
A membership function 301 manages subscribers and service information about MBMS service users and performs the function of authority verification for user terminal (UE) requesting activation of MBMS service. Further, it generates billing information on MBMS service users.
A session and transmission function 302 performs a schedule management and control function for sessions constituting MBMS service or retransmission sessions, and allocates a Temporary Multicast Group Identifier (TMGI) identifying an arbitrary MBMS service. In addition, it performs the role of transferring MBMS service data by maintaining transport between the GGSN and the BM-SC based on service quality (QoS) information or information such as MBMS service area. It is also required to provide proper schemes that can be endured against errors, such as specialized MBMS codecs required for delivery of multimedia contents and Forward Error Correction (FEC) methods, to authenticate all resources to acquire contents from external CP/MB source servers and authenticate an access thereto, and to accept contents from them.
A proxy and transport function 303 is in charge of an agent function that relays control signals and traffic transport between the GGSN and the internal functions of the BM-SC. If BM-SC functions for different MBMS services are distributively provided to multiple physical network elements, the proxy and transport function 303 enables the GGSN that is the gateway of the mobile communication network to constantly maintain access points regardless of the internal structure of the BM-SC. Thus, with the proxy function, the routing for interactions of diverse signals between the internal functions of the BM-SC and the GGSN becomes transparent to the GGSN. Further, the proxy and transport function 303 generates a billing record for billing in connection with the use of data transmitted.
A service announcement function 304 performs the function of announcing service information for multicast and broadcast service to an area where the service will be provided. The service announcement function has to offer to the user terminal (UE) media specifications (for example, video and audio encoding format) describing information on media distributed as part of one MBMS user service, and to offer to the user terminal MBMS session specification describing information for MBMS session distributed as part of MBMS user service such as multicast service identifier, address system, transmission time, etc. The service announcement in the service announcement function 304 should be triggered by the BM-SC as the function of user service level, but is not necessary to be sent by the BM-SC and may conform to a separate method.
As methods that may be applied for service announcement, there may be a method using an MBMS bearer announcing MBMS user service, a push method (WAP push), a method using URL, a point to point method using SMS, and an SMS-CB (Cell Broadcast).
The BM-SC can use a security function 305 of authentication for MBMS service users and for integrity and secrecy protection of MBMS data. In order for only rightful users to participate in MBMS user service, the authentication and authority verification for users are required, and for stable data transfer, a transmission traffic protection function is required. Among these, the authority verification for MBMS service is performed by the membership function 301 that is one of the major functions of the BM-SC and a series of functions necessary for user authentication and information protection functions are provided through the MBMS security function 305. The security function executes the generation, management and distribution of keys to be used for authentication and information protection of users, wherein the keys are periodically varied to prove that they are not defective.
The CP/MB source server 306 provides discontinuous or continuous media as well as service specifications and control information to the BM-SC that offers services through MBMS broadcast multicast bearer services at a particular time. The MBMS user service can simultaneously use one or more MBMS delivery methods. Also, the CP/MB source server 306 can be supplied by a third party, and exists within a provider network or can be supported outside the provider network. The CP/MB source server 306 is operated by linking with the session and transmission function 302 for information delivery and its related information delivery.
FIG. 4 is a view for explaining control signals and traffic linking between the GGSN that is the gateway of the mobile communication network and the BM-SC to provide an MBMS service.
There are eight pairs of control signal procedures between the GGSN and the BM-SC, wherein theses procedures are associated organically with each other or operated independently.
An authentication request and an authentication response 401 and 402 are control signals generated when a certain mobile terminal tries to join in a multicast group for MBMS service, and are requested towards the BM-SC from the mobile communication network. The BM-SC verifies suitability for service desired by a user terminal and provides GGSN information to offer the desired service.
A registration request and a registration response 403 and 404 are a procedure which, if judged as a suitable user in the authentication step, is executed to register the GGSN to support the user terminal in the multicast group tree, and are requested towards the BM-SC from the mobile communication network. If the GGSN was already registered for the target service, this procedure is not taken place and its execution or non-execution is determined by the GGSN.
A session start request and a session start response 405 and 406 is a procedure that is carried out to request the mobile communication network to set an MBMS bearer to which the corresponding service contents are to be delivered when the MBMS service registered in the BM-SC arrives at the start time. These are requested towards the mobile communication network by the judgment of the session management function within the BM-SC. The BM-SC requests the GGSN that belongs to the multicast tree for the target service to make a session setting, and prepares contents to be delivered through the set bearer. If the session start request and the session start response have bee finished, the BM-SC transfers the MBMS service traffic to the registered GGSN area to receive the target service (417).
A session stop request and a session stop response 407 and 408 are a procedure that occurs when the contents delivered by the session start procedure are finished or a service stop time arrives. This procedure releases the MBMS bearer set for the target service and stops the traffic delivery for service. The session start procedure and the session stop procedure mean only the start and end of traffic delivery, but do not mean the addition and elimination of multicast tree or user for the target service and service information.
A leave indication and a UE removal request 409 and 410 are a procedure that happens when a subscriber who belongs to the multicast group for a service escapes from the corresponding service group, and are requested towards the BM-SC from the mobile communication network. The BM-SC checks whether the requested user belongs to the corresponding service group and returns the result.
A deactivation indication and a deactivation confirmation 411 and 412 are a procedure that eliminates, when it is judged in the leave indication and UE removal request 409 and 410 procedure that the requested user belonging to the multicast group of the target service is a rightful subscriber, the user from the multicast group tree, and are requested towards the BM-SC from the mobile communication network. The deactivation indication/deactivation confirmation procedure is performed only when the execution result of the leave indication and UE removal request procedure is successful, and the corresponding terminal after this procedure can no longer receive contents although the service again starts.
A common deregistration request and response 413 and 414 procedure is a procedure that is performed to eliminate the corresponding GGSN from the multicast tree stored in the BM-SC when the information of a terminal escaping from the multicast group tree indicates a last terminal out of terminals belonging to the arbitrary GGSN after the leave indication and UE removal request 409 and 410 procedure and the deactivation indication and deactivation confirmation 411 and 412 procedure are executed, and is requested towards the BM-SC from the mobile communication network. The execution or non-execution of this procedure is determined by the GGSN.
A BM-SC initiated deregistration request and response 415 and 416 procedure is a procedure that, when the GGSN where no registered terminal exists is still within the multicast group tree a predetermined time after the deactivation indication and confirmation 411 and 412 procedure has been finished, the BM-SC finding the above status instructs the mobile communication network to eliminate the corresponding GGSN from the multicast group tree. This procedure happens due to the result of the abnormal process, and the above status is found when checking if the GGSN that should be naturally eliminated from the multicast group tree still remains therein, and is managed to prevent unnecessary signaling or traffic induction.
Independently from these procedures, it is required to perform a procedure of announcing an MBMS service list to be offered by specific areas before the procedures. This is achieved through the MBMS service announcement 418 procedure. The service announcement function can be executed through various types of internet applications and can also be delivered through the MBMS broadcast and multicast bearer. In case of delivering it through the bearer, a separate MBMS bearer setting procedure is required to deliver the service announcement information and this is requested by the BM-SC through the use of the session start request procedure. Once the separate MBMS bearer setting for delivery of service announcement has been finished in the mobile communication network, the BM-SC periodically delivers various information, required for receiving the supportable service list and target service by areas, in the form of data.
The MBMS service as discussed above increases the load of the BM-SC by a change of service environment because the mobile communication networks that are distributed in the MBMS service areas having the relationship therebetween are managed and controlled through one BM-SC.
Under the situation that the transmission rate nearly reaches the level of a wired network due to the development of wireless transmission technology, services requiring more quick and superior performance are being increased, and customized services in which various multimedia contents are provided for more subdivided user groups are being increased for value creation of mobile communication service. The increase in the number of services and diversity of service types increase service resources to be managed by the BM-SC and makes session and traffic transmission management constituting services complicated. In addition, many subscribers cause the activation and deactivation processes for MBMS service and increase the frequency of addition/elimination to/from the multicast service group by movement between MBMS service areas and between the mobile communication networks, and sessions activated per unit time are many and mutual linking procedures with external contents providers are increased.
The change of this service environment increases the processing load of the BM-SC, and thus, there is a need for a scheme capable of improving the capacity and performance of the BM-SC for provision of continuous and stable MBMS services.